Ppt of salient features of viral nucleic acid

Virology salient features of viral nucleic acid

1. SALIENT FEATURES OF
VIRAL GENETIC MATERIAL
SALIENT FEATURES OF
VIRAL GENETIC MATERIAL

2. DRASHTI GAJJAR
IU2446530011
Bachlor of science
Bsc Microbiology Hons
Sem - 3
IISHLS
Virology
Aastha Bariya Ma'am

3. INTRODUCTION
Viruses are non-cellular, obligate intracellular parasites that cannot
reproduce on their own.
They consist mainly of nucleic acid (DNA or RNA) enclosed within a
protein coat (capsid); some also have an envelope.
Viral nucleic acids carry the genetic instructions required for
replication and infection.
Unlike living cells, viruses lack metabolic machinery and depend
completely on the host cell for energy, enzymes, and ribosomes.
The study of viral nucleic acids helps in understanding their diversity,
pathogenicity, and use in medicine/biotechnology.

4. Viruses classified based on genetic material
Types: DNA viruses, RNA viruses, Retroviruses
Genome may be: single or double stranded, linear or circular, segmented or non-segmented
DNA Viruses
Genome: DNA
Types:
Double-stranded DNA (dsDNA): Herpesvirus
Single-stranded DNA (ssDNA): Parvovirus
Shape: Linear or circular
Stable, low mutation rate
TYPES OF GENETIC MATERIAL

5. RNA Viruses
Genome: RNA
Types:
Positive-sense ssRNA (+ssRNA): Acts as mRNA directly
Examples: Poliovirus, Hepatitis A, Coronaviruses
Negative-sense ssRNA (–ssRNA): Needs RNA-dependent RNA polymerase
Examples: Rabies, Influenza, Measles
Double-stranded RNA (dsRNA): Segmented genome, requires RNA
polymerase
Example: Rotavirus
High mutation rate → rapid evolution
Retroviruses
Genome: ssRNA
Use reverse transcriptase → DNA intermediate
DNA integrates into host genome (provirus)
Example: HIV TYPES OF GENETIC MATERIAL

6. DNA / RNA Viral genomes are unique because they contain only
one type of nucleic acid
A virus can have DNA or RNA, but never both together
in the same particle
This feature sets viruses apart from cellular
organisms, which always carry both DNA and RNA
The nature of the nucleic acid (DNA or RNA) is a key
factor in classification of viruses (Baltimore system)
Determines viral replication mechanism, mutation
rate, and stability

7. POLARITY OF RNA GENOMES Positive-sense RNA (+RNA): Functions directly as
mRNA → can be immediately translated by host
ribosomes
Negative-sense RNA (–RNA): Cannot be directly
translated → requires RNA-dependent RNA
polymerase to produce complementary +RNA
Polarity determines how quickly viral proteins are
synthesized and how replication begins
Example:
+RNA → Poliovirus
–RNA → Influenza virus

8. Viral genomes may exist in two forms:
Single-stranded (ss)
Double-stranded (ds)
1. DNA Viruses:
dsDNA viruses → Most common (e.g., Herpesvirus, Poxvirus, Adenovirus)
ssDNA viruses → Less common, must form dsDNA before replication (e.g.,
Parvovirus)
2. RNA Viruses:
ssRNA viruses → Most abundant; can be positive-sense (+) or negative-sense
(–)
(+)ssRNA: Functions directly as mRNA (e.g., Poliovirus, Coronaviruses)
(–)ssRNA: Requires RNA-dependent RNA polymerase (e.g., Rabies,
Influenza)
dsRNA viruses → Rare, segmented genomes (e.g., Rotavirus) SINGLE-STRANDED OR DOUBLE-STRANDED

9. Viral genomes show different physical
organizations
Linear genomes: Adenoviruses,
Herpesviruses, Poxviruses
Circular genomes: Papillomaviruses,
Polyomaviruses, some bacteriophages
Segmented genomes: Influenza virus (8
RNA segments), Rotavirus (11 RNA
segments)
Genome arrangement influences
replication, reassortment, and
diversity LINEAR, CIRCULAR, OR SEGMENTED

10. Viral genomes are much smaller than those of cellular organisms
Range: ~2 kilobases (kb) to >200 kilobases (kb)
Smallest viral genomes:
Circoviridae (~2 kb, only a few genes)
Parvoviridae (~5 kb)
Largest viral genomes:
Poxviridae (>200 kb, encode >200 proteins)
Mimivirus (~1.2 megabases, rivaling small bacteria)
Genome size directly influences:
Number of proteins encoded
Dependence on host cell machinery (smaller genomes rely more on host)SMALL GENOME SIZE

11. LIMITED CODING CAPACITY
Viral genomes are small and cannot code for all life functions
Encode only essential proteins, mainly:
Structural proteins → capsid, envelope glycoproteins
Non-structural proteins → enzymes (polymerases, proteases), regulatory
proteins
Rely heavily on the host cell machinery for:
DNA/RNA synthesis
Protein translation
Energy and metabolic processes
Example: Poliovirus genome (~7.5 kb) encodes just a few proteins, while host
provides rest

12. HIGH VARIABILITY RNA viruses mutate rapidly due to lack of
proofreading in RNA polymerases
DNA viruses are more stable, but can still undergo
mutations
High variability helps viruses:
Adapt quickly to new hosts
Evade immune responses
Develop drug resistance
Example: Frequent antigenic drift in Influenza virus

13. ANY QUERIES ?THANK YOU!!